Conversion of hydrocarbons



Filed Nov. 18, 1959 DU Bols Exs'nyluw ET Al.

CONVERSION OF HYDROCARBONS Oct. l5, 1940.

Patented Oct. 15, 1940 CONVERSION 0F HYDROC'ARBONS Du Bois Eastman and Charles Richker, Port Arthur, Tex., assignors to The Texas Company, a corporation of Delaware Application November 18, 1939, Serial No. 305,100

9 Claims.

This invention relates to the conversion of hydrocarbons for the' production of gasoline or motor fuel and is concerned particularly with certain novel improvements in combination cracking processes.

The invention contemplates a method of processing raw charging stock such as crude petroleum stocks to ultimate yields of gasoline or motor fuel in which the charging stock is fractionated to separate residual constituents from lighter fractions, in which the residual constituents are subjected to cracking or viscosity-breaking With the aid of a lstream of highly heated condensate to effect conversion into gasoline constituents as Well as into a large yield of intermediate constituents adapted for further conversion into gasoline, in which the cracked or viscositybroken products are fractionated to separate gasoline constituents from higherboiling components adapted for further cracking, in which lighter fractions from the raw charging stock as Well as the intermediate constituents obtained from the cracking or Viscosity-breaking of the heavy residual constituents are subjected to cracking for conversion into gasoline and in Which'a portion of the reflux condensate obtained in the fractionation of the resulting cracked products is subjected to cracking in a recycling cracking zone While another portion of such a reflux condensate constitutes the stream of highly heated products that is combined With the residual constituents to accomplish the cracking or viscositybreaking thereof.

The gasoline ordinarily produced in the viscosity-breaking of crude residues is of materially lower anti-knock qualitythan that which can be produced by the cracking of condensate stocks and consequently the lower anti-knock quality of the gasoline from the viscosity-breaking operation operates to reduce the anti-knock value of the total gasoline produced in a combination cracking process. It is an object of the present invention to raise the anti-knock quality of the gasoline obtained in the Viscosity-breaking operation andv this object. is accomplished by highly heating a portion of the reux condensate obtainedfrom-.the cracked products and combining the heated products'with the residual constituents so as to raise the temperature of the latter and increase the rate of cracking per pass to which the residual constituents are subjected so as to thereby increase the anti-knock quality of the gasoline produced, yWhile the other portion of the reflux condensate is passed to a separate cracking coil for conversion. In a preferred embodiment of the invention,v the com-i'A bined residual constituents and highly heated condensate are in contact in one or morereaction chambers in which liquid is prevented from accumulating so that While unvaporized cornponents are subjected to cracking the time of reaction is limited by the rapid Withdrawal of the liquid components from the reactionzone l While vaporized constituents are permitted a longer time of reaction. In this Way high rates of cracking per pass may be applied in the cracking or viscosity-breaking of vthe residualstock With the avoidance of coking diculties.'

In accordance With the invention the crude petroleum is fractionated to obtain a residue and;

condensate stocks, such as gas oil, kerosene and naphtha, Which it is desired to subject to crack,-l

ing for conversion into gasoline constituents or for reforming of gasoline constituents into products of higher anti-knock quality. The toppedf.y

or reduced crude may be introduced into a fractionating zone which receives' vapors from rthe primary cracking or viscosity-breaking operation and a resultant mixture of unvaporized residue and heavy reiiux condensate is passed through L a heating zone wherein it is heated to a cracking temperature and then delivered to ya reaction zone. The straight-run naphtha or gas oil, or such mixtures thereof as it may be desired to and subjected to cracking. The resultant cracked products are separated into vaporsand residue andthe vapors fractionated to form a reflux condensate, the major portion of which is passed to a recycling cracking coil. A minor portion crack or reform, are passed to a'crackingzonell of such reflux condensate is passed to a separate s As a further feature of obtaining, in the combination process contemplated by the invention,

ultimate yields of gasoline or motor. fuel from the original crude charging stock, the' invention has in View the recovery from the normallygase- I ous products produced in the process of fractions,y particularly C3 and C4 hydrocarbons adapted for cracking and polymerizing reactions for the production of normally liquid hydrocarbons,'and the cycling of such normally gaseous constituents to certain cracking zones of the process wherein conditions are maintained suitable not only for conversion of normally liquid hydrocarbons into lower boiling liquid hydrocarbons but also suitable for polymerizing and reversion reactions adapted to increase the yield of products in the gasoline boiling range. In accordance with the invention the crude oil stock is fractionated to separate residual constituents from lighter fractions, the residual constituents and lighter fractions are subjected to separate cracking treatments while a normally gaseous hydrocarbon fraction recovered from the cracked products is subjected to polymerization or reversion in contact with products undergoing cracking.

For the purpose of more fully disclosing the invention, reference is had to the accompanying drawing which is a flow diagram illustrating a particular embodiment of the invention.

In the apparatus shown in the drawings, crude oil, after being heated by heat exchange with hot products of the process, or otherwise heated to a desired distilling temperature, is introduced by pump I5 to a distilling and fractionating tower I I which is provided with such fractionating elements and such cooling or reuxing means as may be necessary to accomplish the desired fractionation of the separated vapors. A plurality of trapout trays, as I2, I3 and E4, may be provided for the collection of such fractions as may be dresired. Uncondensed vapors may pass to a condenser coil I5 and the distillate may be collected in a receiving drum or gas separator l5. Typical fractions collected in the fractional distillation are gas oil, collected in tray I 2, kerosene, collected in tray I3, naphtha collected in tray I4 and a naphtha or gasoline distillate collected in the accumulator I5. It is often desired to remove a kerosene or burning oil fraction to be marketed as such and -a line Il is indicated for the withdrawal of such fraction from the tray I3.

Lines I8, I9 and 2l) extend from trapout trays I 2, I3 and I4, respectively, to a common manifold line 2I leading to a pump 22 by which any or all of the fractions may be delivered through a line 23 to a heating coil 24 positioned in a heating Zone or furnace 275 adapted for heating the oil to a cracking temperature. The cracked products from the heating coil 25 pass through transfer line v2G to a separator or reaction chamber 2'I in which separation of vapors from liquid residue takes place.

The separated vapors pass to a fractionator 28 which is provided with conventional fractionating elements and with such cooling or refluxing means as may be desired. Reflux condensate is drawn from tower 28 through a line 29 and delivered by a pump 3U through a line 3l to heating coil 32 positioned in a heating zone or furnace 33 adapted to heat the oil to a cracking temperature. The cracked products from the heating coil 32 pass through a transfer line 34 to the separator or reaction chamber 2l.

The line 3! is provided with a branch line 35 leading to a heating coil 35 disposed in a heating zone or furnace 37 adapted to heat the oil to a cracking temperature The cracked products from heating coil 36 pass through a transfer line 38 to the upper end of a reaction chamber 39. Theproducts of reaction are drawn from the lower end of reaction chamber 39 and passed through a transfer linellii to the upper 'end of a second reaction chamber 4I; the products from reaction chamber 4I are drawn from the bottom thereof and pass through a transfer line 42 to a separating zone 43 of a combined separating and fractionating tower 42. It is desirable to pass the major portion of the reflux condensate from tower 28 to the cracking coil 32 and utilize as small a proportion as possible to aid in the cracking or vis cosity-breaking of the crude residuum. The eX- act amount required to be passed to heating coil 36 depends upon the temperature to which the cycle condensate can be heated in the coil 35 without coking trouble therein or in the transfer line and the temperature desired to be maintained in the reaction chambers. It is recommended that about 20 %-30% of the condensate be passed to the heating coil 35, thus leaving 70%-80% for passage to the cracking coil 32. The cracked products separate into vapors and residue in a separating Zone 43 of tower 42, the residue from which separating Zone may be withdrawn through a line 45, while the separated vapors pass upwardly for fractionation in the upper portion of the chamber, this upper portion being provided with conventional fractionating elements and with such cooling and refluxing means as may be desired. A trapout tray 46 is provided fol' the collection of reflux condensate.

Topped or reduced crude is withdrawn from the crude oil stripping tower II by a pump 4l by which the residue is pumped through a line 48 to the fractionating section of tower 42 above the tray 46 to dephlegmate the vapors therein. The resulting mixture of unvaporized residue and reflux condensate is directed by a pump 49 to heating coil 5I] positioned in a heating zone or furnace 5I adapted to heat the oil to a cracking temperature. The cracked products pass from the heating coil through a transfer line 52 which merges with the transfer line 28 so as to intimately commingle the products from the heating coil 50 with the products passing from the heating coil 36. The commingled products flow downwardly through reaction chambers 39 and 4I in succession thence to the separating zone 43,

Uncondensed vapors pass from tower 42 to a condenser coil 53 and the distillate is collected in a receiving drum or gas separator 54. The distillate is drawn by a pump 55 and directed through a line 56 to the tower 28 so that intermediate constituents produced in the cracking or viscosity-breaking of the residual constituents of the crude charging stock may thus be combined with intermediate constitu-ents in the tower 28 for passage to the cracking coil 32.

Residue from separator 2'I is drawn through a line 51 which may have a pressure reducing valve 58 and is conducted to a ash drum 55. The line 45 through which residue is withdrawn from separator 43 also leads to the ash drum 59 and the line 45 may be provided with a pressure reducing valve 60. In the drum 59 vapors separate from residue and the residue is withdrawn through a line 6I. The overhead vapors pass to a condenser coil 62 and the distillate is collected in a receiving drum or gas separator 53. Distillate from the drum 63 is withdrawn by a pump 64 and conducted through a line 65 to the fractionating section of the tower 42 for refractionation therein and so that heavier flashed constituents may be combined with the mixture of residual constituents and reiiux condensate which is passed to the cracking coil 50 while lighter constituents may be condensed in cooler 53 and collected in accumulator 54 for passage to the fractionator 28 so as to thus combine ashed constituents with the reflux condensate being cycled to cracking coil 32. The line 65 may have a branch line 66a so that a portion or all of the ashed condensate may be directed to line 56 and thus introduced directly to the tower 28. Ordinarily, it is better, however, to pass all of the flashed distillate to the fractionating section of tower 42 since the flashed distillate will contain large proportions of heavy constituents which are more suitably subjected to cracking in the cracking coil 50 together with the residual constituents undergoing reaction therein, rather than in the cracking coil 32,

Gases separated out in the accumulator 54 are removed through a line 66 and may be conducted by pump or compressor 61 to the separator 21 or fractionator 28. The compressor discharge line 68 may conveniently extend to the line 5S so that the gases may be introduced into the tower 28. It is advantageous to provide a cooling coil and separator in the line 68 so that `only liquefied components, particularly C3 and C4 hydrocarbons, may be directed to the tower 28-while lighter constituents, particularly hydrogen and methane, may be removed from the system. The gas line 66 may conveniently have a branch line 10 leading to a pump or compressor 1 I so that in an alternative operation the gases may be delivered to an absorber 12. The line 65 may be provided with a branch line 13 leading to a cooling coil 14 so that a portion of the ashed condensate may be diverted to the cooling coil and passed thence through a line 15 to the absorber 12 to constitute an absorbent menstruum therein. Unabsorbed gases, such as hydrogen and methane, may be removed through a line 16a while the menstruum containing absorbed gases, particularly C3 and C4 hydrocarbons, may be con-ducted by pump 'I5 and line 16 thence to the line 56 for introduction to the fractionator 28.

`Uncondensed vapors and gases from the'fractionator 28 pass to a condenser coil 11 and the distillate is collected in a receiving drum or gas separator 18 having a gas line 19. A relatively high pressure is preferably maintainedon the receiving drum 18 so that the distillate collecting therein may contain maximum proportions of C3 and C4 hydrocarbons and so that minimum proportions of C'a and C4 hydrocarbons will pass out with the lighter gases throughthe gas line 19. The distillate is drawn from accumulator 18 by a pump 80 and directed to a rectifying tower 8| which is equipped with conventional fractionating elements and with such reboiling means and cooling or reiuxing means as may be desired. The rectiiied distillate is withdrawn through a line 82. Uncondensed gases pass to a condenser coil 83 thence to a receiving drum or gas separator 84 in which the liquefied product, comprising largely C3 and C4 hydrocarbons, is separated from lighter hydrocarbons which are removed as a gas through `a line B5. The liquefied normally gaseous fraction is withdrawn by pump or compressor B6 and delivered through a line 81 to the cycle condensate line 3| so that the normally gaseous hydrocarbons may be commingled with the condensate passing to the cracking coils 32 and 36 for polymerizing and reversion reactions therein. In cases where it is desired to introduce the normally gaseous fraction to one of the cracking coils 32 or 36 and not to the other, or tointroduce different proportions of the normally gaseous fraction to these coils, the line 81 may communicate directly either with the line35, or with the line 3| beyond the point of its junction with the line 35. The line 81 may be provided with branch line 88 so that a portion or all of the pressures of about 200to 400 pounds.

normally gaseous fraction may be directed to the cracking coil 24 for contact with the straightrun condensate being subjected to cracking there- `in and for polymerizing or reversion reactions therein. k

In practicing the invention the fractional distillation of the crude oil may be conducted at approximately atmospheric pressure or at superatmospheric pressures, such as 25 to 125 pounds, with temperatures in the bottom of the fractionator Il of from about 500 F. to 700 F., the exact temperature depending upon the extent of distillation desired. For example, when it is desired to separate out a gas oil cut in the tower I I for subsequent cracking, a relatively high temperature such as 650 F. or '100 F. may be employed. When it is desired to distill ofi' only naphtha and kerosene in the tower Il less heating of the crude oil is required for the distillation in the tower II and the ga's oil fraction desired for cracking may be distilled off from the crude residue in the tower 42 by means of the hot Vapors from reaction chamber 4I. Temperatures of 900 F. to 1100 F. under 200 to 1000 pounds pressure are recommended for the single-pass cracking coil 24 and temperatures of 900 F. to 1100" F. under 200 to '750 pounds pressure for the recycling cracking coil 32. High rates of cracking per pass, such as rates of %40%, as measured by conversion into 400 endpoint gasoline, are recommended for the single-pass cracking coil 24 while the rates of cracking per pass in the recycling cracking coil 32 will be generally lower, such as 15 %20%. The reaction chamber 21 should be held under about 200 to 400 pounds pressure with temperatures ordinarily of 750 F. to 850 F. in the bottom of the chamberand of '100 F. to 800 F. in the top of the chamber. 'I'he condensate ywhich is passed to heating coil 36 is heated therein to temperatures of 900 F. 'to 1100 F. under pressures of 200 to 800 pounds. The mixture of heavy reflux condensate and unvaporized crude residuum which is drawn from tray 46 of tower 42 and passed to the heating coil 50 is subjected therein to temperatures of 850 F. to 950 F. under pressures of 200 to 800 pounds. The heated streams from the heating coils 36 and 50 are combined for further cracking in reaction chambers 30 and 4I wherein temperatures, preferably as high as 850 F. and ordinarily not exceeding about 930 F, are maintained under If desired, the cracked products from the reaction chambers may be separated into'vapors and residue with I will be about 650 F. to 750 F. and the temperatures in the top of tower 42 will run approximately 500 F. to 600 F. or 650 F. The fractionator 28 is preferably held under approximately the same pressure as that of the reaction chamber 21 with temperatures of 700 F. to 800 F. in the bottom and temperatures of 400 F. to 550 F. at the top. The receiving drum 18 should be held under relatively high pressure such as 200 pounds or even higher to insure-that a minimum of C3 and C4 hydrocarbons will be released with the lighter gases through the gas line 11 and so that there will be a maximum retention of the C3 and C4 hydrocarbons in the distillate which is passed to the stabilizer 8|. The temperaturepressure conditions for stabilizing the gasoline distillate will vary with the particular stabilized product desired but generally speaking the stabilization should be conducted under pressures of 200 to 400 pounds with bottom temperatures of 350 F. to 400 F. and top temperatures of 100 to 200 F. In the ash drum the pressure should be reduced to within a range of 25 to 100 pounds with temperatures of 700 F. to 800 F. therein. The absorber I2 is preferably held under pressures as high as 200 pounds, pressures of 220 to 250 pounds being recommended at normal ternperatures or at temperatures of F. to 220 F.

In a typical example of the invention, crude oil is fractionally distilled to recover a light gasoline product collected in receiver i6, a heavy naphtha fraction collected in tray lll having an initial boiling point of about 250 F. to 350 F. and an endpoint of about 500 F. and a kerosene fraction withdrawn from tray I3. The crude residue containing gas oil constituents is introduced into the tower t2 wherein the residue is further heated and vaporized so that gas oil constituents, particularly the lighter gas oil constituents from the crude, pass overhead from the tower and are collected as a part of the distillate accumulating in receiver 54. The unvaporized crude residuum combined with heavy reflux condensate is withdrawn from tray 45 at a temperature of '740 F. and directed to cracking coil 50 wherein it is subjected to a cracking temperature of 900 F. under a pressure of about 400 pounds at the outlet of the heating coil. Approximately 20% of the reflux condensate from tower 28 is passed through line 35 to the heating coil 30 wherein the condensate is subjected to cracking at a temperature of 1000 F. under a pressure of about 400 pounds in the heating coil outlet. The products from the two cracking coils 35 and 50 are combined for further cracking in reaction chambers 39 and il which are maintained under about 400 pounds pressure with a temperature of 920 F. in reaction chamber 30 and 910 F. in reaction chamber :'H. rIhe remaining 80% of the reux condensate from the tower 2B is subjected to cracking in the heating coil 32 at a temperature of 980 F. under 600 pounds pressure. Normally gaseous hydrocarbons from receiver 84 consisting predominantly of C3 and C4 hydrocarbons are combined with the straight-run heavy naphtha and subjected to reforming and reversion reactions in the heating coil 23 at a temperature of 1050 F.

under 800 pounds pressure.

In a second example of the invention crude residue withdrawn from the tower il at a temperature of r700" F. is directed into tower 42 for further heating and vaporization. rIhe mixture of unvaporized residue and heavy reflux condensate is withdrawn from tray 40 at a temperature of 780 F. and directed to cracking coil 50 wherein it is subjected to a cracking temperature of 900 F. under a pressure cf about 400 pounds at the outlet of the heating coil. Ihe products from cracking coil 50 are combined with the hot products from cracking coil 36 for further cracking in reaction chambers 30 and M, which are maintained under conditions similar to that of the preceding example. A straight-run kerosene fraction is withdrawn from tray I3 and a naphtha fraction, withdrawn from tray ill and having a boiling range similar to that of the preceding example, is combined with the gas oil fraction withdrawn from tray l2 having an endpoint of about '700 F. The combined naphtha and gas oil fractions are mixed with normally gaseous hydrocarbons from receiver 84 consisting predominantly of C3 and C4 hydrocarbons and the mixture is subjected to a cracking temperature in the coil 24 of 1050 F. under 800 pounds pressure to eiect conversion of gas oil constituents into gasoline constituents as well as to effect reforming of gasoline constituents and polymerization and reversion of normally gaseous constituents to form normally liquid hydrocarbons of the gasoline boiling range. The reflux condensate from tower 28 is divided as in the previous example, a portion passing to the heating coil 36 and the other portion being subjected to cracking in the cracking coil 32 under conditions similar to that of the preceding example.

In each of the preceding examples the residue withdrawn from reaction chamber 31 is flashdistilled, the flash distillate is refluxed in tower i2 and the distillate from receiving drum 50 is refluxed in the tower 28. The normally gaseous fraction from receiver 54 is either placed under compression and resulting compressed constituents delivered to the tower 28 or such normally gaseous fraction is delivered to the absorber 'l2 into which a portion of the flashed distillate, which has been cooled, is introduced and the menstruum containing the absorbed hydrocarbons is delivered to the fractionator 28.

In any of the preceding examples the normally gaseous fraction withdrawn from accumulator 84 by pump 86 may be directed to the recycling cracking coil 32 instead of to the cracking coil 2d for polymerizing and reversion reactions with the cycle condensate undergoing reaction.

In any of the preceding examples the normally gaseous fraction withdrawn from accumulator 84 by pump 86 may be subjected to a separate cracking operation at high cracking temperatures of the order of 1100 F. to 1200" F. to increase the olefmic content of the gases prior to passing the gases to either of the cracking coils 24 or 32.

When cycling the normally gaseous hydrocarbon fraction to the heating coil 36, it is ordinarily desirable to maintain relatively high pressures in the heating coil 36 or in both the heating coil 3E and reaction chambers 39 and 4|. In one advantageous operation in accordance with the invention, the process is conducted substantially as has been described in the rst and second examples of the invention, except that the normally gaseous fraction to be subjected to polymerizing and reversion reactions is directed to the heating coil 36 in which the mixture of cycle condensate and normally gaseous hydrocarbons are subjected to a temperature of about 1000 F. under a pressure of 800 or 1000 pounds and the cracking and conversion is continued in the reaction chambers under pressures of about 600 to 800 pounds and at temperatures of the order of 900 F.

Although a preferred embodiment of the invention has been described herein, it will be understood that various changes and modifications may be made therein, while securing to a greater or less extent some or vall of the benefits of the invention, without departing from the spirit and scope thereof.

We claim:

l. The process of cracking hydrocarbons that comprises fractionating a crude petroleum stock to separate residual constituents from lighter 75 constituents, heating such residual constituents to a cracking temperature, passing such lighter constituents to a cracking zone wherein they are heated to a cracking temperature under superatmospheric pressure and subjected to conversion, separating the resultant cracked products into vapors and residue, passing the separated vapors to a fractionating Zone wherein fractionation takes place to separate a reflux condensate from lighter fractions, directing a portion of said reflux condensate to a cracking Zone wherein it is heated to a cracking temperature under superatmospheric pressure and subjected to conversion, separating the resultant cracked products of the latter cracking operation into vapors and residue and passing resultant separated vapors to the aforesaid fractionating zone, directing another portion of said reflux condensate to a heating zone wherein it is heated to a cracking temperature under superatmospheric pressure, combining the resultant heated products from said heating Zone with the heated residual constituents to thereby raise the temperature of the residual constituents and subjecting the admixed products to further cracking in a reaction zone wherein cracking conditions of temperature and pressure are maintained, separating the products of the latter cracking into vapors and residue and combining resultant vaporized constituents with the aforesaid reux condensate for cracking therewith.

2. The process of cracking hydrocarbons that comprises fractionating crude petroleum stock to separate a residual fraction from a lighter fraction, introducing said residual fraction into a fractionating zone in contact with hot vapors therein and wherein fractionation takes place to separate lighter fractions from heavy reflux condensate admixed with unvaporized constituents of said residual fraction, passing the mixture of heavy reflux condensate and unvaporized residual constituents to a heating Zone wherein the mixture is heated to a cracking temperature under superatmospheric pressure, combining the resultant heated mixture with a stream of hot products from a separate heating zone to thereby raise the temperature of said mixture and subjecting the combined products to further cracking in a reaction zone wherein cracking conditions of temperature and pressure are maintained, separating the resultant products of the latter cracking into vapors and residue and passing the separated vapors to the aforesaid fractionating zone, directing said lighter fraction, obtained from the fractionation of the crude petroleum stock, to a cracking zone wherein it is heated to cracking temperature under superatmospheric pressure and subjected to conversion, separating the resultant products of the latter cracking into vapors and residue and passing the separated vapors to a second fractionating zone wherein fractionation takes place to separate reflux condensate from lighter fractions, directing a portion of said reflux condensate toa recycling cracking zone wherein it is heated to a cracking temperature under superatmospheric pressure and subjected toconversion, separating the resultant products of the recycling cracking operation into vapors and residue and passing the separated vapors to said second fractionating zone, directing another portion of said reflux condensate to said separate heating zone wherein it is heated to `a cracking temperature under superatmospheric pressure and utilizing the resultant heated products as said stream of hot products with which said heated mixture of residual constituents and heavy reiiux condensate is combined as aforesaid, and combining lighter fractions from the first-mentioned fractionating Zone with reflux condensate formed in the second fractionating zone for cracking therewith.

3. The process of cracking hydrocarbons that comprises fractionating a crude petroleum stockk to separate residual constituents from lighter constitutents, heating such residual constituents to a cracking temperature, passing such lighter constituents to a cracking zone wherein they are heated to a cracking temperature under superatmospheric pressure and subjected to conversion, separating the resultant cracked products into vapors and residue, passing the separated vapors to a fractionating zone wherein fractionation.

takes place to separate a reflux condensate from lighter fractions, directing a portion of saidreux condensate to a cracking Zone wherein it is heated to a cracking temperature under superatmospheric pressure and subjected to conversion, separating the resultant cracked products' of the latter cracking operation into vapors and residue and passing resultant separated vapors to the aforesaid fractionating zone, passing another portion of said reflux condensate in a stream through a heating zone wherein it is heated to a cracking temperature under superatmospheric pressure, combining the resultant heated products from said heating zone with the heated residual constituents to thereby raise the temperature of the residual constituents and passing the admixed products downwardly through a reaction zone wherein cracking conditions of ternperature and pressure are maintained, removing products from said reaction zone at a rate adequate to prevent the accumulation of liquid therein and separating the resultant cracked products into vapors and residue, and combining resultant vaporized constituents with the aforesaid reflux condensate for cracking therewith.

4. The process of cracking hydrocarbons that comprises fractionating crude petroleum stock to separate a residual fraction from a lighter fraction, introducing said residual fraction into a fractionating zone in contact with hot vapors therein and wherein fractionation takes place to separate lighter fractions from heavy re-lux condensate admixed with unvaporized constituents of said residual fraction, passing the mixture of heavy reflux condensate and unvaporized residual constituents to a heating zone wherein the mixture is heated to a cracking temperature under superatmospheric pressure, combining the resultant heated mixture with a stream of hot products from a separate heating zone to thereby raise the temperature of the mixture and passing the admixed products downwardly through a reaction Zone wherein cracking conditions of temperature and pressure are maintained, removing products from said reaction Zone at a rate adequate to prevent the accumulation of liquid therein, passing hot cracked vapors from said reaction zone to the aforesaid fractionating Zone, directing said lighter fraction, obtained from the fractionation of the crude petroleum stock, to a cracking zone wherein it is heated to cracking temperature under superatmospheric pressure and subjected to conversion, separating the resultant products of the latter cracking into vapors and residue and passing the separated vapors to a second fractionating zone wherein fractionation takes place to separate reflux condensate from lighter fractions, directing a portion of said reux condensate to a recycling cracking zone wherein it is heated to a cracking temperature under superatmospheric pressure and subjected to conversion, separating the resultant products of the recycling cracking operation into vapors and residue and passing the separated vapors to said second fractionating Zone, directing another portion of said reflux condensate to said separate heating zone wherein it is heated to a cracking temperature under superatmospheric pressure and utilizing the resultant heated products as said stream of hot products with which said heated mixture of residual constituents and heavy reflux condensate is combined as aforesaid, and combining lighter fractions from the first-mentioned fractionating zone with reflux condensate formed in the second fractionating Zone for cracking therewith.

5. The process of cracking hydrocarbons that comprises fractionating a crude petroleum stock to separate residual constituents from lighter constituents, heating such residual constituents to a cracking temperature, passing such lighter constituents to a cracking zone wherein they are heated to a cracking temperature under superatmospheric pressure and subjected to conversion into lower boiling products, separating the resultant cracked products into vapors and residue, passing the separated vapors to a fractionating zone and subjecting the vapors therein to fractionation to form a reflux condensate, a lighter distillate product and heavier and lighter normally gaseous hydrocarbon fractions, introducing said heavier normally gaseous hydrocarbon fraction into the aforesaid cracking Zone in contact with said lighter constituents from the crude petroleum for reaction therein, directing a portion of said reflux condensate to a cracking zone wherein it is heated to a cracking temperature under superatmospheric pressure and subjected to conversion into lower boiling products, separating the resultant cracked products into vapors and residue and passing resultant separated vapors to the aforesaid fractionating zone, directing another portion of said reux condensate to a heating zone wherein it is heated to a cracking temperature under superatmospheric pressure, combining the resultant heated products from said heating zone with the aforesaid heated residual constituents to raise the temperature of the residual constituents and subjecting the admixed products to further cracking in a reaction zone wherein cracking conditions of temperature and pressure are maintained, separating the products of the latter cracking into vapors and residue and combining resultant vaporized constituents with the aforesaid reflux condensate for cracking therewith.

6. The process of cracking hydrocarbons that comprises fractionating a crude petroleum stock to separate residual constituents from lighter constituents, heating such residual constituents to a cracking temperature, passing such lighter constituents to a cracking zone wherein they are heated to a cracking temperature under superatmospheric pressure and subjected to conversion into lower boiling products, separating the resultant cracked products into vapors and residue, passing the separated vapors to a fractionating zone and subjecting the vapors therein to fractionation to form a reflux condensate, a lighter distillate product and heavier and lighter normally gaseous hydrocarbon fractions, combining a portion of said reflux condensate with said heavier normally gaseous hydrocarbon fraction and subjecting the mixture to conversion conditions of temperature and pressure to effect conversion into hydrocarbons of the gasoline boiling range, separating the resultant cracked products into vapors and residue and passing resultant separated vapors to the aforesaid fractionating zone, directing another portion of said reflux condensate to a heating zone wherein it is heated to a cracking temperature under superatmospheric pressure, combining the resultant heated products from said heating zone with the aforesaid heated residual constituents to raise the temperature of the residual constituents and subjecting the admixed products to further cracking in a reaction zone wherein cracking conditions of temperature and pressure are maintained, separating the products of the latter cracking into vapors and residue and combining resultant vaporized constituents with the aforesaid reux condensate for cracking therewith.

'7. The process of cracking hydrocarbons that comprises fractionating a crude petroleum stock to separate residual constituents from lighter constituents, heating such residual constituents to a cracking temperature, passing such lighter constituents to a cracking zone wherein they are heated to a cracking temperature under superatmospheric pressure and subjected to conversion into lower boiling products, separating the resultant cracked products into vapors and residue, passing the separated vapors to a fractionating zone and subjecting the vapors therein to fractionation to form a reflux condensate, a lighter distillate product and heavier and lighter normally gaseous hydrocarbon fractions, directing a portion of said reiiux condensate to a cracking zone wherein it is heated to a cracking temperature under superatmospheric pressure and subjected to conversion, separating the resultant cracked products of the latter cracking operation into vapors and residue and passing resultant separated vapors to the aforesaid fractionating zone, combining another portion of said reflux condensate with said heavier normally gaseous hydrocarbon fraction and heating the mixture in a heating zone to a cracking temperature under superatmospheric pressure, combining the resultant heated products from said heating Zone with the heated residual constituents to thereby raise the temperature of the residual constituents and subjecting the admixed products to further cracking in a reaction zone wherein cracking conditions of temperature and pressure are maintained, separating the products of the latter cracking into vapors and residue and combining resultant vaporized constituents with the aforesaid reflux condensate for cracking therewith.

8. The process of cracking hydrocarbons that comprises fractionating a crude petroleum stock to separate residual constituents from lighter constituents, heating such residual constituents to a cracking temperature, passing such lighter constituents to a cracking zone wherein they are heated to a cracking temperature under superatrnospheric pressure and subjected to conversion into lower boiling products, separating the resultant cracked products into vapors and residue, passing the separated vapors to a fractionating zone and subjecting the vapors therein to fractionation to form a reux condensate, a lighter distillate product and heavier and lighter normally gaseous hydrocarbon fractions, directing a portion of said reux condensate to a cracking Zone wherein it is heated to a cracking temperature under superatmospheric pressure and subjected to conversion, separating the resultant cracked products of the latter cracking operation into vapors and residue and passing resultant separated vapors to the aforesaid fractionating Zone, combining another portion of said reflux condensate With said heavier normally gaseous hydrocarbon fraction and heating the mixture in a heating zone to a cracking temperature under superatmospheric pressure, combining the resultantl heated products from said heating zone with the heated residual constituents to thereby raise the temperature of the residual constituents and passing the admixed products downwardly through a reaction Zone wherein cracking conditions of temperature and pressure are maintained, removing products from said reaction Zone at a rate adequate to prevent the accumulation of liquid therein and separating the resultant cracked products into vapors and residue, and combining resultant vaporized constituents with the aforesaid reflux condensate for cracking therewith.

9. 'Ihe process of cracking hydrocarbons that comprises fractionatingcrude petroleum stock to separate a residual fraction from lighter constituents, introducing said residual fraction into a ractionating Zone in Contact with hot vapors therein and wherein fractionation takes place to form a heavy reflux condensate admixed with unvaporized constituents of said residual fraction, lighter condensate constituents and a fraction comprising normally gaseous hydrocarbons, passing the mixture of heavy reflux condensate and unvaporized residual constituents to a heating Zone wherein the mixture is heated to a cracking temperature under superatmospheric pressure, combining the resultant heated mixture with a stream of hot products from a separate heating zone to thereby raise the temperature of said mixture and subjecting the combined products to further cracking in a reaction zone wherein cracking conditions of temperature and pressure are maintained, separating the resultant products of the latter cracking into vapors and residue and passing the separated vapors to the a1`oresaid fractionating zone, directing lightei1 constity uents, obtained from the fractionation of the crude petroleum stock, to a cracking Zone Wherein it is heated to a cracking temperature under superatmospheric pressure and subjected to conversion, separating the resultant products ci the latter cracking into vapors and residue, passn ing the separated vapors to a second fractionating zone and subjecting the vapors therein to fractionation to form a reux condensate, a lighter distillate product and heavier and lighter normally gaseous hydrocarbon Vfractions, combining such heavier normally gaseous hydrocarbons with said lighter constituents -from the fractionation ,of the crude petroleum stock for conversion therewith in the aforesaid.v cracking zone, directing a portion of said reux condensate to a recycling cracking zone wherein it is heated to a cracking temperature under superatmospheric pressure and subjected to conversion, separating the resultant products of the recycling cracking operation into vapors and residue and passing the separated vapors to said second fractionating zone, directing anothery portion of said reuX condensate to said separate heating zone wherein it is heated to a cracking temperature under superatmospheric pressure and utilizing the resultant heated products as said stream of hot products with which said heated mixture of residual constituents and heavy reiiux condensate is combined as aforesaid, combining lighter condensate constituents from the rst-mentioned iractionating zone with reflux condensate formed in the secondk fractionating Zone and directing normally gaseous hydrocarbons from the first fractionating zone to the second fractionating zone.

DU BOIS EASTMAN. CHARLES RICHKER. 

